To increase the speed and capacity of optical communications, a ROADM (Reconfigurable Optical Add/Drop Multiplexer) technology has recently been devised. An optical network of the ROADM uses a wavelength division multiplexing transmission system, and is capable of branching and inserting optical signals having any wavelengths without converting the optical signals to electrical signals. In addition, in the optical network of the ROADM, when changing, newly adding, or removing a route through which an optical signal of each wavelength should pass, it is possible to change the route, that is, to reconfigure the route (reconfigurable), without conducting works such as a connecting work.
Achieving the ROADM requires a switch apparatus (also called a multi-cast switch) capable of inputting and outputting a plurality of wavelengths and also capable of changing routes. Specifically, the switch apparatus used for the ROADM has a function of receiving an input of an optical signal from a client device and inserting the optical signal into a pathway of the ROADM network as well as a function of outputting to the client device an optical signal branched from a pathway of the ROADM network. The switch apparatus is capable of dynamically changing a route through which an optical signal passes.
FIG. 9 is a top view of one example of a switch apparatus 900 used for the ROADM. The switch apparatus 900 has two sets of configurations in each of which the number of routes (the number of pathways) on the ROADM network side is 8 and the number of routes (the number of wavelengths) on the client device side is 16. The switch apparatus 900 includes two splitter units 920 and eight switch units 930 in a housing 960. Each of the splitter units 920 includes a predetermined number of optical splitters, and each of the switch units 930 includes a predetermined number of optical switches. One end of each splitter unit 920 is connected to the ROADM network through a network-side fiber 940, and the other end thereof is branched to be connected to one ends of the switch units 930. Moreover, the other end of each switch unit 930 is connected to a client device through a client-side fiber 950. Meanwhile, FIG. 9 does not illustrate wiring among the splitter units 920, the switch units 930, the network-side fibers 940, and the client-side fibers 950, for the sake of simplification. Such configuration allows for branching and insertion of optical signals between the ROADM network and the client device.
Desired numbers of pathways and wavelengths can be obtained by changing the numbers of the splitter units 920 and the switch units 930 included in the switch apparatus 900, as well as, the number of branches of the optical splitters included in each splitter unit 920 and the number of branches of the optical switches included in each switch unit 930.
In the switch apparatus 900 illustrated in FIG. 9, to increase the number of supported wavelengths, the number of the switch units 930 needs to be increased. This increases the area required to arrange the switch apparatus 900, and also increases manufacturing costs due to increases in the amounts of materials required for the manufacture. To handle a larger number of wavelengths, there are demands for reduction in size and reduction in costs of a switch apparatus.